1. Field of the Invention
The present invention is concerned with semiconductor elements, e.g., semiconductor bridge elements, which are surface-connectable and may optionally have polarity-independent electrostatic discharge protection, with devices including such semiconductor elements, and to methods of making such elements and devices. More particularly, the present invention is concerned with a semiconductor element having an electrically conductive coating extending from the top to the bottom surface thereof, a semiconductor element protected against electrostatic discharge by back-to-back zener diodes, methods of manufacturing such elements, and methods of manufacturing devices including the same.
2. Related Art
Semiconductor bridge ("SCB") elements (sometimes herein referred to as "chips") and means to electrically connect them for the purpose of electrical activation are well-known in the art. Presently, both the SCB of U.S. Pat. No. 4,708,060, to Bickes, Jr. et al, issued Nov. 24, 1987, and the tungsten bridge SCB of U.S. Pat. No. 4,976,200 to Benson et al, issued Dec. 11, 1990, are manufactured with large metalized pads for electrical contact to the active area of the bridge. The SCB chip generally is mechanically bonded to an attachment surface (of a header or other element) with epoxy adhesive. The standard electrical connection is then made to the top of the chip by wire-bonding, that is, by attaching wires from the metalized lands of the chip to the appropriate electrical contacts of the header. Proper functioning of the SCB in a detonator requires intimate contact with an energetic material such as an explosive or pyrotechnic material, and this demands an upright position for the chip; that is, the chip cannot be assembled with its active area positioned against the header, but its active area must face towards and contact the energetic material so that the active area is free to interact with the energetic material.
International Pat. WO 94/19661 to Willis, published Sep. 1, 1994, discloses a wrap-around conductive layer which is manufactured by cutting a channel in the wafer, metal plating the wafer, etching the bottom of the wafer and then metal plating the back. U.S. Pat. No. 5,080,016 to Osher, issued Jan. 14, 1992, discloses a conductor which wraps around the dielectric block and occupies the entire back surface thereof.
The prior art also provides for protecting SCB chips against electrostatic discharge. The SCBs of U.S. Pat. No. 5,179,248 to Hartman et al, issued Jan. 12, 1993, and of U.S. Pat. No. 5,309,841 to Hartman et al, issued May 10, 1994, are manufactured with large metalized pads to provide electrical contacts for energizing the active area of the bridge. These patents also show the use of a single zener diode (in discrete or on-chip integrated form) connected in parallel with the SCB for protection against unwanted electrostatic discharge ("ESD")and EMI voltages.
U.S. Pat. No. 5,327,832 to Atkeson, issued Jul. 12, 1994, shows unbiased discharge protection for a three conductor field-effect transistor. U.S. Pat. No. 5,500,546 to Marum, issued on Mar. 19, 1996, discloses multiple diodes for electrostatic discharge protection. However, these components are located in a separate control circuit for the operational circuitry.
It would be desirable to provide a surface-connectable SCB which can be easily manufactured with intrinsic, unbiased ESD protection.